Q1.(30 pts) In the lectures we have seen through an example that forward and backward chaining can be combined to produce a kind of mixed chaining. Suppose that another method uses the following procedure:

The default method of chaining is always backward chaining.

Rules are not partitioned according to whether there is a priority according to forward or backward chaining.

Whenever a rule is fired, the premises of all remaining rules are examined to if they may be fired (i.e. we revert to forward chaining). If so, they are fired. If not, we continue backward chaining.

Use this procedure to deal with the following rule set used in the lectures http://ari.cankaya.edu.tr/~agorur/AI/AI/~ceng462/303/lect/chp7.html#7.5

R.1 IF F AND H THEN K

R.2 IF E AND A THEN K

R.3 IF E AND B THEN H

R.4 IF A AND G THEN B

R.5 IF B AND D THEN H

R.6 IF G AND D THEN E

R.7 IF A AND B THEN D

R.8 IF A AND C THEN G

Note that K is the final goal and backward chaining would normally start with R.1. However, since A and C are both known prior to the consultation session, we may immediately fire R.8 to begin the process.

Q.3(60 pts). You are just starting a quiet evening at home when an old friend calls to announce he is coming over for?? dinner at your place. This being a big surprise, you immediately undertake emergency dinner preparations.

??????????? Within a few minutes, you have managed to load up the BARTENDER expert system on your PC so that you can select a drink.

??????????? BARTENDER is a backward?chaining production system with rules given below. Note that when more than one rule has a consequent matching the current problem, those rules are tried in the order given in the list.

Rule 1:???? IF???? expensive wine is selected

??????? ??????? AND??? it is 31st of December

??????? ??????? THEN?? champagne

Rule 2: ??? IF???? expensive wine is selected???

??????? ??????? AND??? first meal is steak

??????? ??????? THEN?? red wine

Rule 3: ??? IF???? cheap wine is selected

?????? ???????? AND??? first meal is chicken

??????? ??????? AND??? guest is not well?liked

??????? ??????? THEN?? apple wine

Rule 4: ??? IF???? cheap wine is selected

??????? ??????? AND??? first meal is unknown

??????????????? THEN?? pink wine

Rule 5: ??? IF???? beer is selected

??????? ??????? AND??? first meal is Mexican beans

??????? ??????? THEN?? Spanish beer

Rule 6: ??? IF??? ?beer is selected

??????? ??????? THEN?? Tuborg

Rule 7: ??? IF???? guest is concerned about his health

??????? ??????? THEN?? Efes?

Rule 8: ??? IF???? guest is concerned about his health

??????? ??????? AND??? carrots are not to be served

??????? ??????? THEN?? carrot juice

Rule 9: ??? IF???? wine is selected

??????? ??????? AND??? guest should be impressed

??????? ??????? THEN?? expensive wine

Rule 10:?? IF???? wine is selected

??????? ??????? THEN?? cheap wine

Rule 11:?? IF???? guest is sophisticated

??????? ??????? THEN?? wine

Rule 12:?? IF???? first meal is Mexican beans

??????? ??????? THEN?? beer

Rule 13:?? IF???? guest is not well?liked

??????? ??????? AND??? first meal is provided by Restaurant X

??????? ??????? THEN?? beer

Rule 14:?? IF???? true

??????? ??????? THEN?? water

BARTENDER's hypotheses are as follows:

???? ? champagne

???? ? red wine

???? ? pink wine

???? ? apple wine

???? ? Spanish beer

???? ? Tuborg

???? ? Efes

???? ? carrot juice

- water

Now here are some facts to assume true, if an inquiry is made:

???? ? first meal is provided by Restaurant X

???? ? first meal is Mexican beans

???? ? guest is not well?liked

???? ? guest is sophisticated

???? ? it is 31st of December

???? ? first meal is chicken

And here are some facts to assume false, if an inquiry is made:

???? ? carrots are not to be served

???? ? first meal is unknown

???? ? guest is concerned about his health??

???? ? guest should be impressed

???? ? first meal is steak

?????????????????????????????????????????????????????

Note that:

???? 1. In working this problem, remember that the BARTENDER program has no means for problem solving except using the rules.

???? 2.? Assume that a user answers questions using BARTENDER's hypotheses given above.

???? 3.? Assume BARTENDER's control structure is such that it never asks the user if an assertion is true if there is any rule with that assertion in its THEN part. If there are such rules, but none verifies the assertion, the assertion is assumed to, be false.

???? 4.? Assume BARTENDER stops when one hypothesis is verified.

????????

PART A

Simulate BARTENDER's behaviour on the given facts. Take care to use the hypotheses in the given order. Indicate your answer by showing the sequence in which the rules fire and the name of the drink selected.

???????? Rule Number???????????????????? Selected Drink

PART B

With some different set of facts, could BARTENDER ever recommend the red wine with Mexican beans? If not, why not?

SOLUTION: (10 pts)

PART C

With some different set of facts, could BARTENDER ever recommend carrot juice with steak? If not, why not??

SOLUTION:(10 pts)

PART D

Assume the existing rule set is added with a collection of meta? rules. Each meta?rule is to be tried, possibly initiating some backward?chaining, before the ordinary process of hypothesis checking and backward?chaining begins. Here are the meta?rules:

M1: ???? IF?? the first meal is chicken

???? ?????? THEN delete rules 12 and 13

M2: ???? IF?? expensive wine is selected

??????? ??? THEN delete rules 2 and 4

?? ???????? AND? replace rule 3 with rule 15 (below)

Rule 15:IF?? cheap wine is selected

????????????? THEN Villa Doluca

??????? ???

Now determine which drink will be selected again given the set of facts to be assumed true. You need only to specify the drink; do not bother to show the order the rules are used.